Development of a Micro-baddeleyite (ZrO2) U-series Chronometer for Recent Mafic Lavas

重建以往火山爆发的爆发前和爆发后年表，对于了解人类对自然灾害的反应模式和制定减轻现有火山灾害的战略至关重要。尽管许多地质年代学技术的成熟适用于日期第四纪火山喷发，相当大的不确定性仍然存在的岩浆过程的时间，最终在激烈的喷发，以及他们的环境影响，即使是相当近的事件。这项研究将为二氧化硅丰度相对较低的常见类型的火山开发一种测年工具，使用现有的计时器很难确定其日期。最后，对这些火山喷发历史的年龄限制的改进将有助于更好地评估火山的危害。新的计时器是基于锆氧化物矿物斜锆石晶格中固有的铀的放射性衰变。斜锆石的晶体尺寸通常很小，因此这项研究将改进电子束技术，以定位岩石中的微斜锆石晶体，并制定分析程序，通过二次电离质谱法分析斜锆石，以检测铀及其放射性衰变产物的痕量丰度。将对有代表性的火山进行调查，以根据其他测年技术校准斜锆石计时器。为此，加州洛杉矶大学的研究人员正在与国内外火山学家合作。案例研究包括喀斯喀特火山（美国）和坎帕尼亚火山省（意大利）的火山。这些火山代表了长期存在的火山系统，具有数万至数十万年的周期性喷发的漫长历史。通过斜锆石铀不平衡定年建立精确的火山年代地层学，最终将有助于更好地了解岩浆产出率和在广泛的岩浆环境中的喷发复发间隔。

Reconstructing the pre- and post-eruptive chronology of past volcanic eruptions is essential for understanding the patterns of human response to natural disasters, and to devise mitigation strategies for extant volcanic hazards. Despite the maturity of many geochronological techniques applied to date Quaternary volcanic eruptions, considerable uncertainties remain with regard to the timing of magmatic processes culminating in violent eruptions, as well as their environmental impact even for fairly recent events. This research will develop a dating tool for common types of volcanoes characterized by comparatively low silica abundances, which can be difficult to date using existing chronometers. Ultimately, improved age constraints on the eruptive history of such volcanoes will lead to better assessments of their volcanic hazards.The new chronometer is based on the radioactive decay of uranium intrinsic to the crystal lattice of baddeleyite, a zirconium oxide mineral. Crystal sizes for baddeleyite are typically small, and therefore this research will improve electron-beam techniques for locating micro-baddeleyite crystals in rocks, and develop analytical procedures to analyze baddeleyite via secondary ionization mass spectrometry to detect trace abundances of uranium and its radioactive decay products. Representative volcanoes will be investigated to calibrate the baddeleyite chronometer against other dating techniques. For this, University of California Los Angeles researchers are collaborating with domestic and international volcanologists. Case studies include volcanoes in the Cascades (USA) and the Campanian volcanic province (Italy). These volcanoes represent long-lived volcanic systems with a protracted history of recurrent eruptions over tens to hundred thousands of years. Establishing precise and accurate volcanic chronostratigraphies through baddeleyite uranium disequilibrium dating will ultimately contribute to an improved understanding of magma output rates and eruptive recurrence intervals in a broad range of magmatic environments.